Add Parse method to PhysicalChunkData

src/ImageSharp/Formats/Png/Chunks/PhysicalChunkData.cs

@@ -37,6 +37,20 @@ namespace SixLabors.ImageSharp.Formats.Png.Chunks
         /// </summary>
         public byte UnitSpecifier { get; }
 
+        /// <summary>
+        /// Parses the PhysicalChunkData from the given buffer.
+        /// </summary>
+        /// <param name="data">The data buffer.</param>
+        /// <returns>The parsed PhysicalChunkData.</returns>
+        public static PhysicalChunkData Parse(ReadOnlySpan<byte> data)
+        {
+            uint hResolution = BinaryPrimitives.ReadUInt32BigEndian(data.Slice(0, 4));
+            uint vResolution = BinaryPrimitives.ReadUInt32BigEndian(data.Slice(4, 4));
+            byte unit = data[8];
+
+            return new PhysicalChunkData(hResolution, vResolution, unit);
+        }
+
         /// <summary>
         /// Constructs the PngPhysicalChunkData from the provided metadata.
         /// If the resolution units are not in meters, they are automatically convereted.
@@ -76,7 +90,7 @@ namespace SixLabors.ImageSharp.Formats.Png.Chunks
                     break;
             }
 
-            return new PngPhysicalChunkData(x, y, unitSpecifier);
+            return new PhysicalChunkData(x, y, unitSpecifier);
         }
 
         /// <summary>

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -8,6 +8,7 @@ using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Formats.Png.Filters;
 using SixLabors.ImageSharp.Formats.Png.Zlib;
 using SixLabors.ImageSharp.Memory;
@@ -376,26 +377,14 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="data">The data containing physical data.</param>
         private void ReadPhysicalChunk(ImageMetaData metadata, ReadOnlySpan<byte> data)
         {
-            // The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image. It contains:
-            // Pixels per unit, X axis: 4 bytes (unsigned integer)
-            // Pixels per unit, Y axis: 4 bytes (unsigned integer)
-            // Unit specifier:          1 byte
-            //
-            // The following values are legal for the unit specifier:
-            //   0: unit is unknown
-            //   1: unit is the meter
-            //
-            // When the unit specifier is 0, the pHYs chunk defines pixel aspect ratio only; the actual size of the pixels remains unspecified.
-            int hResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(0, 4));
-            int vResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(4, 4));
-            byte unit = data[8];
-
-            metadata.ResolutionUnits = unit == byte.MinValue
+            var physicalChunk = PhysicalChunkData.Parse(data);
+
+            metadata.ResolutionUnits = physicalChunk.UnitSpecifier == byte.MinValue
                 ? PixelResolutionUnit.AspectRatio
                 : PixelResolutionUnit.PixelsPerMeter;
 
-            metadata.HorizontalResolution = hResolution;
-            metadata.VerticalResolution = vResolution;
+            metadata.HorizontalResolution = physicalChunk.XAxisPixelsPerUnit;
+            metadata.VerticalResolution = physicalChunk.YAxisPixelsPerUnit;
         }
 
         /// <summary>

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -9,6 +9,7 @@ using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Formats.Png.Filters;
 using SixLabors.ImageSharp.Formats.Png.Zlib;
 using SixLabors.ImageSharp.Memory;